LAKE    SUPERIOR   REGION.  233 
Nos.  1,  2,  and  3,  above,  are  paralleled  in  Finland  by  similar  rocks 
in  similar  order,  as  described  by  Sederholm.  Kocks  corresponding  to 
No.  4,  the  Lower  Keewatin,  seem  to  be  wanting,  or  are  seen  only  as 
inclusions  in  the  next  younger  granite. 
It  is  probable  that  the  divisions  above  detailed  for  Minnesota  and 
Finland  are  wholly  embraced  in  the  lower  division  of  the  Canadian 
Laurentian,.  i.  e.,  in  the  Ottawa  gneiss,  and  that  they  have  not  yet 
been  noted  in  Canada.  The  fundamental  gneiss  of  Canada  is,  there- 
fore, not  the  bottom  of  the  geological  series,  but  is  largely  a  sedi- 
mentary series  derived  from  an  older  series,  this  older  series  being  in 
part  at  least  a  greenstone,  as  indicated  by  the  stratigraphic  succession 
in  Minnesota. 
Winchell  (N.  H.),190  in  1898,  discusses  the  Archean  greenstones 
of  Minnesota,  which  he  considers  the  oldest  known  rocks,  represent- 
ing the  original  crust  of  the  earth.  The  greenstones  are  divisible  into 
two  parts,  one  igneous  and  the  other  clastic,  the  latter  succeeding  the 
former  with  a  confused  and  apparently  sometimes  conformable  su- 
perposition, somewhat  as  surface  eruptive  rocks  might  be  superposed, 
in  the  presence  of  oceanic  action,  upon  a  massive  of  the  same  nature  at 
the  same  place.  The  clastic  portions  of  the  greenstones  vary  to  more 
siliceous  rocks,  constituting  great  thicknesses  of  graywackes,  phyllites, 
and  conglomerates,  and  as  such  have  been  converted  by  widespread 
metamorphism  into  mica  schists  and  gneisses. 
As  the  Laurentian  gneisses  and  granites  cut  the  schists  and  sedi- 
mentary gneisses  they  are  also  younger  than  the  bottom  greenstones. 
The  metamorphic  schists  and  gneisses  seem  to  be  representative  of 
the  sedimentary  portion  of  the  Lower  Laurentian  of  Canada,  while 
the  igneous  granite  and  gneisses  are  as  plainly  a  general  parallel  of  the 
igneous  portion  of  that  series.  It  follows,  therefore,  that  the  Cana- 
dian Laurentian  is,  as  a  whole,  of  later  date  than  the  greenstones,  if 
the  succession  is  the  same  as  in  the  Northwest,  and  that  the  green- 
stones should  be  considered  the  bottom  rock  of  the  geological  scale. 
Winchell  (N.  H.),200  in  1898,  discusses  the  significance  of  the 
fragmental  eruptive  debris  at  Taylors  Falls,  Minn.  This  has  hereto- 
fore been  regarded  as  a  conglomerate  resting  unconformably  upon  the 
Keweenawan.  As  a  result  of  recent  field  work  by  C.  P.  Berkey,  it  is 
believed  that  this  conglomerate  may  be  separated  into  two  conglom- 
erates— an  upper  one  at  the  base  of  the  upper  division  of  the  Cam- 
brian and  a  lower  one  at  the  base  of  the  lower  division.  The  latter 
would  come  within  the  Keweenawan,  as  this  term  is  used  by  Irving 
and  other  writers,  and  would  separate  this  series  into  two  parts.® 
The  later  conglomerate  rests  directly  upon  the  earlier  one,  leading  to 
the  previous  confusion  of  the  true  relations.     Similar  conglomerates 
"  In  a  recent  paper,  summarized  on  p.  192,  Berkey  (Am.  Geologist,  vol.  20,  1897,  p.  381) 
takes  the  view  that  the  lower  conglomerate  is  a  How  breccia  of  the  igneous  rocks. 
